The present invention relates to an improved injection molding apparatus including power units therefor, and more particularly an injection molding apparatus having reduced noise emissions and reduced vibration transmission, plus an improved method for reducing noise emission and vibration transmission in an injection molding apparatus.
U.S. Pat. No. 5,707,667 by Galt, Kestle and Yetter teaches an improved sound insulated injection molding machine including at least one hydraulic pump and an electric motor means for powering said pump. It is desirable to provide further improvements in the reduction of noise emission and vibration transmission.
Injection molding machines that use hydraulics as a primary source of power transfer are all faced with the problem of noise and vibration generated by the hydraulic system. The problem manifests itself in three ways: fluid borne noise; structural or mechanical borne noise; and air borne noise. All three of these may be addressed in various ways, which include both mechanical and hydraulic modifications. However, reduction in noise emission and vibration transmission represents a long sought after goal.
The hydraulic power source in an injection molding system is one or more hydraulic pumps driven by an electric motor. The pumps are structurally connected to the electric motor, as with an adapter flange, with the rotational drive being provided by a rotary coupling. The electric motor and hydraulic pump assembly are supported on vibration dampening pads, which are in turn fastened to the injection molding machine base.
A characteristic of hydraulic pumps is that they have a high power density. This means that the electrical power of the electric motor is converted to hydraulic power in a small package. Part of this energy conversion requires that low pressure hydraulic fluid is brought up to a high level of pressure in a very short time. This quick rise of pressure is accomplished on many small volumes of oil within the pump in short succession. This in turn creates high frequency pressure pulses in both the high pressure outlet of the pump and the low pressure inlet of the pump. The housing of the pump also vibrates due to these pulses.
The pressure pulses in the suction and pressure lines of the pump create not only fluid borne noise but mechanical vibrations in the suction and pressure lines. These vibrations are transmitted to the machine reservoir and base, and also to the structure that supports the pump and motor assembly, which is normally part of the machine base and which will be referred to herein as a"drip pan".
The machine reservoir, base and drip pan are usually fabricated of the same material. For most applications this material is steel, which can be of welded, formed or cast construction. The disadvantage of using the same material throughout the base structure is that it will then inherently have the same natural frequency. It is desirable to reduce vibration transmission in these structures by designing the structures with suitable materials of different natural frequencies since this will make the transmission of vibration energy less efficient.
The structural transmission of vibration energy may also be reduced by adding damping elements and masses in series between the vibration energy source and the vibration energy dissipater, i.e., the side of the reservoir which converts some of the structural vibration energy to air borne vibration energy or sound. The larger the masses are in this system, the less efficient the energy transfer becomes.
Hot and cold rolled steel is also highly reflective to air borne sound energy. In efforts of noise reduction in the area of the hydraulic pumps, the majority of the air borne noise will simply reflect off any of the structure fabricated from steel. This would include the drip pan area under the pumps as well as the side of the reservoir and base. It would be desirable to utilize a suitable material that has the ability to absorb sound energy rather than one that reflects sound energy.
Accordingly, it is a principal object of the present invention to provide an improved injection molding apparatus which includes a power source and which has reduced noise emission and vibration transmission characteristics, as well as an improved method for mounting power components to an injection molding apparatus.
It is a further object of the present invention to provide an improved apparatus and method as aforesaid which is simple, convenient, inexpensive and effective.
Further objects and advantages of the present invention will appear hereinbelow.